Radiation monitoring of a physical property of a material

ABSTRACT

Apparatus and assembly for and associated method of monitoring a physical property of a material, such as the specific gravity of a processed meat product of the density, and hence weight, of tobacco in a cigarette rod, comprising: means ( 19 ) arranged to direct radiation ( 30 ) into a material having a physical property to be monitored; first sensing means ( 23 ) arranged to sense levels of residual measurement radiation passing from the irradiated material and to provide respective measurement signals representative of the sensed levels of residual measurement radiation; reference means ( 18 ) which is arranged to be located in the path of the radiation ( 30 ), optionally adjacent or within the material whose physical property is to be monitored, and which has radiation absorption characteristics corresponding to predetermined low and/or high radiation absorption characteristics of the material whose physical property is to be monitored; second sensing means ( 22 ) arranged to sense levels of residual reference radiation passing from said irradiated reference means and to provide reference signals representative of said sensed levels of residual reference radiation; and means ( 130 ) arranged to process the measurement and reference signals, to provide interpolated measurement signals which are corrected to take into account any variable operating parameters of the apparatus and which are representative of the actual monitored physical property. The invention also provides a method of calibrating the apparatus on an on-going basis.

DESCRIPTION

This invention relates to the monitoring of a physical property of amaterial, such as the specific gravity (density) of a manufactured meatproduct or the density, and hence weight, of tobacco in a “cigaretterod” of constant cross-sectional area, using a penetrative ordiffractive radiation, for example an X-ray beam, and measuring itsabsorption by the material whose physical property is to be measured, todetermine such property.

The invention has particular application in the meat processingindustry, as well as other product processing industries, for example,the tobacco, pharmaceutical and plastics processing industries.

Typically, a material of which a physical property, such as the specificgravity, is to be monitored, is placed in the path of a beam ofradiation, for example, an X-ray beam, to produce a signal at a sensoror an array of sensors representative of the value of the physicalproperty which is dependent upon the amount of radiation absorbed by theproduct and, hence, the residual amount of radiation received by thesensor(s).

In the meat processing industry, the monitoring of the specific gravityof a meat product slurry or emulsion of various particle sizes can beused to determine changes in the proportion of fat within the product.Because the difference in specific gravities gives rise to only a verysmall signal variation using conventional techniques, it has been foundnecessary to develop a technique for monitoring the specific gravity ofprocessed meat products to a greater accuracy than previously.

In the tobacco industry, weight control of cigarettes has beendetermined traditionally by monitoring the beta ray absorption of thecigarette at the point where it has been formed into a “rod”. Thistechnique forms part of a closed loop system for maintaining consistencyin the weight of the cigarettes, which is particularly important in viewof the high cost of tobacco products. At present, the application ofradioactive sources, such as that for generating beta rays, is becomingincreasingly undesirable due to the regulatory considerations associatedwith the handling and disposal of such sources.

In the pharmaceutical industry, similar monitoring techniques are usedfor the accurate determination of the weight of dispensed powder drugsor tablets in containers, such as blister packs.

Also, in the medical industry, similar monitoring techniques are usedfor the accurate determination of quantities of dressings in packs.

Further, in the food industry, similar monitoring techniques are usedfor the accurate determination of product presence and/or mass.

However, in all the present radiation absorption monitoring techniques,the resulting signal(s) produced by the sensor(s) due to the receiptthereby of the residual radiation which has not been absorbed by theproduct, is influenced by several operating parameters which can varyindeterminately during the monitoring process. Such variable operatingparameters include, in the case of radiation absorption monitoringtechniques, the acceleration voltage applied to the radiation generator,for example, an X-ray beam generator, the radiation beam current of thegenerator and, in the vast majority of cases, changes in the ambienttemperature of the monitoring environment.

These variations in such operating parameters, as well as others, duringthe monitoring process result in inaccurate monitoring measurements,which is undesirable if the physical property of the product is to bedetermined accurately.

Generally, it is difficult to stabilise some or all of these parametersto a degree which is sufficient to provide the required accuracy ofphysical property monitoring.

Several solutions have been proposed to the problems associated with themonitoring of a property of a material. For example, Johnson, in hisUnited State patent (U.S. Pat. No. 4,504,963), proposes a system foranalysing meat in which a sample of meat is placed in a sample containerwhich is irradiated with X-rays, the attenuated beam being detected andcompared with a previously determined calibration. The signal of theattenuated beam is related to the fat content of the meat and therebyprovides a measure of the fat content of the meat.

Hauni Mascinenbau AG in their European patent (EP0790006) propose an“on-line” analysis method in which X-rays are utilised to monitor thedensity of a cigarette rod as it passes the apparatus. It is taught thatan absolute measure of tobacco density nay be effected by continuouslymonitoring the dark signal of a detector element, the fill signal(un-attenuated beam) with a detector element, and the beam strengthafter passage through slices of the cigarette rod. The dark signal andfill signal are used to correct the readings of the other detectorelements which monitor the beam through respective slices of thecigarette rod. In this fashion the apparatus provides an absolutemeasure of the density of tobacco.

Molins PLC, in their International patent application (WO 97/29654),disclose further apparatus for monitoring tobacco density in a cigaretterod in which a reference sample, a “dummy” cigarette, is irradiated withX-rays and the signal derived therefrom is used to control the X-rayemitter so as to ensure a constant output therefrom. By ensuring suchconstant output, the signal which is derived from the detector whichmeasures the beam strength following passage of the X-rays through thecigarette rod is related to the density of the tobacco in the rod.

Accordingly, it is an object of the present invention to provideapparatus and an associated method, which overcomes, or at leastsubstantially reduces, the disadvantages discussed above in relation toknown radiation absorption techniques for monitoring a physical propertyof a manufactured product.

Thus, a first aspect of the invention resides in dual calibrationapparatus for “on-line” or continuous monitoring of a physical propertyof a material, such as the specific gravity of a processed meat productor the density, and hence weight, of tobacco in a cigarette rod, theapparatus comprising:

(a) means arranged to direct radiation into a material having a physicalproperty to be monitored;

(b) first sensing means arranged to sense levels of residual measurementradiation passing from the irradiated material and to provide respectivemeasurement signals representative of said sensed levels of residualmeasurement radiation;

(c) reference means which is arranged to be located in the path of theradiation, optionally adjacent or within the material whose physicalproperty is to be monitored, and which has radiation absorptioncharacteristics corresponding to predetermined low and high radiationabsorption characteristics of the material whose physical property is tobe monitored:

(d) second sensing means arranged to sense levels of residual referenceradiation passing from said irradiated reference means and to providereference signals representative of said sensed levels of residualreference radiation,

(e) means arranged to process the measurement and reference signals, toprovide interpolated measurement signals; and

characterised in that, said reference means comprises a pair of spacedreference standards, a low radiation absorption characteristic standardwhose absorption characteristic corresponds to a minimum level of thephysical property to be monitored and a high radiation absorptioncharacteristic standard whose absorption characteristic corresponds to amaximum level of the physical property to be monitored, the interpolatedresults being corrected to take into account any variable operatingparameters of the apparatus and being representative of the actualmonitored physical property.

In accordance with a second aspect of the invention, there is provided amethod of “on-line-” or continuous monitoring a physical property of amaterial, such as the specific gravity of a processed meat product orthe density, and hence weight, of the tobacco in a cigarette rod, whichmethod comprises;

directing radiation into a material having a physical property beingmonitored;

sensing levels of residual measurement radiation passing from theirradiated material;

providing measurement signals representative of said sensed levels ofresidual measurement radiation;

locating in the path of the radiation, optionally adjacent or within thematerial whose physical property is being monitored, reference meanshaving radiation absorption characteristics corresponding topredetermined low and/or high radiation absorption characteristics ofthe material whose physical property is to be monitored;

sensing the level of residual reference radiation passing from saidirradiated reference means;

providing reference signals representative of said sensed levels ofresidual reference radiation;

processing the measurement and reference signals to provide interpolatedmeasurement signals; and

characterised in that, said reference means comprises a pair of spacedreference standards, a low radiation absorption characteristic standardwhose absorption characteristic corresponds to a minimum level of thephysical property to be monitored and a high radiation absorptioncharacteristic standard whose absorption characteristic corresponds to amaximum level of the physical property to be monitored, and correctingthe interpolated results to take into account any sensed variation ofthe operating parameters and thereby representing the actual monitoredphysical property.

In both aspects of the invention defined above, the radiation employedis preferably X-rays generated by a suitable X-ray source which, in thepreferred embodiment to be described hereinbelow, provides a divergingX-ray beam directed at and into the material, as well as at and into thereference means.

Also, in the case of the inventive apparatus, the first sensing meansfor sensing levels of residual measurement radiation passing from theirradiated material and for providing measurement signals representativeof those sensed residual measurement radiation levels, may be of anysuitable form. In the preferred embodiment to be described hereinbelow,such first sensing means may comprise an X-ray detector capable ofproviding measurement signals representative of the residual measurementlevels of X-rays received thereby from the irradiated material whosephysical property is to be monitored.

Again, and in the case of the inventive apparatus defined above, thepair of spaced reference elements indicated above, may be of anysuitable form, for example, an X-ray detector capable of providingreference signals representative of the levels of residual referenceradiation received thereby.

The two spaced reference elements may each have its own second sensingmeans, possibly incorporated with the first sensing means, for examplein a single array. In such a case, respective measurement and referencesignals from all three sensing means can be processed, by suitableprocessing means, to provide interpolated measurement signalsrepresentative of the actual physical property of the material inquestion. In this manner, any operating parameters of the inventiveapparatus, assembly and method which vary during the monitoring processand which can influence, in an undesirable manner, the sensed levels ofresidual measurement radiation from the material are “calibrated out”using the reference signals, to provide a true value for the monitoredphysical property of the material.

At least insofar as the parameter of the material to be monitored isconcerned, the radiation absorption characteristic of the material ofthe reference means such as the reference elements to be discussedhereinbelow, is preferably very close to or substantially the same asthat of the material whose physical property is to be monitored.

Periodically, the pair of spaced reference elements, whose radiationabsorption characteristics correspond respectively to predetermined lowand high radiation absorption characteristics of the material whosephysical property is to be or is being monitored, can be calibratedabsolutely. For example, in the inventive monitoring apparatus, theradiation source and at least the second sensing means can be moved fromthe vicinity of the material chamber to a position where pre-certifiedcalibration elements can be moved into the path of the radiation, forexample, into the X-ray beam, between that source and the sensor means.Such calibration elements are certified to correspond to predeterminedlow and high percentage tolerance levels of the radiation absorptioncharacteristics of the material in question and are used to calibrateout any medium or long term drift which may have occurred in thereference means located in the path of the radiation during themonitoring process. This arrangement may also be used to calibrate thelinearity of the monitoring apparatus and assembly, particularly thesignal processing means thereof.

Additionally or alternatively, such calibration may be facilitated by aseries of certified references which can be indexed through the X-ray orother radiation beam by means of a motorised mechanism

Also, such calibration can be programmed to occur at predetermined timeintervals.

Preferably, the geometry of at least those components of the inventiveapparatus and assembly involved in the monitoring method is symmetricalor substantially so, in order to maintain uniform radiation of thesensing and reference means.

Further, it is to be understood that although X-ray radiation ispreformed, other types of suitable radiation may be employed in theinventive apparatus, assembly and method described above.

In order that the invention may be more fully understood, a preferredembodiment of monitoring apparatus in accordance with the first aspectof the invention for monitoring the fat content of a processed meatproduct, will now be described by way of example and with reference tothe accompanying drawing in which:

FIG. 1 to a front elevation of a monitoring unit incorporating theinventive apparatus; and

FIG. 2 is a side elevation of the unit of FIG. 1, showing respectiveoperating and calibrating positions of some components of the apparatus.

Referring firstly to FIG. 1 of the drawing, a unit, indicated generallyat 1, for monitoring the specific gravity of a processed meat productwhich is dependent upon the variable fat content of the product,comprises a generally rectangular support cabinet 2 mounted upon fouradjustable legs 3 at respective lower corners thereof. Mountedtransversely of the upper region of the cabinet 2 is a manifoldindicated generally at 11 and comprising an inlet 12, an outlet 13, achamber 14 which is intermediate the inlet 12 and outlet 13 and whichcommunicates therewith via respective conduits 15, 16.

A processed meat product in the form of a meat emulsion can be pumpedthrough the manifold 11 from left to right when the inlet 12 isconnected to the outlet (not shown) of a meat processing machine.

The internal cross section of the chamber 14 is substantially uniform,such that the meat emulsion being pumped therethrough is also ofsubstantially uniform cross section.

Located on respective opposed front and rear sides of the chamber 14 isa pair of sub-chambers 17 in each of which is mounted a referenceelement 18, as shown in FIG. 2 and as described in more detailhereinbelow.

Mounted in the support cabinet 2 below the manifold 11 but in-line withthe chamber 14 and sub-chambers 17, is an X-ray source 19. The powersupply, and associated control equipment, for the X-ray source 19 ismounted in the lower region of the cabinet 2, as shown generally at 20in FIG. 1.

Mounted in the cabinet 2 above the manifold 15 but in-line with thechamber 14 and sub-chambers 17, as well as the X-ray source 19, is anX-ray sensor array indicated generally at 21 and having respective outerportions 22 and an inner portion 23 for detecting X-rays, as will alsobe described in more detail hereinbelow.

In operation of the unit 1, the inlet 12 of the manifold 11 is connectedto the outlet of meat processing equipment and the outlet 13 of themanifold 11 is connected to any suitable equipment for furtherprocessing or packaging of the meat emulsion.

The emulsion is pumped, from left to right, through the manifold 11 andthe X-ray source 19 directs a diverging X-ray beam, as shown at 30 inFIG. 2, into the chamber 14 through which the emulsion is being pumpedand through the sub-chambers 17 in which the reference elements 18 aremounted.

The reference elements 18 are made of any suitable, stable,non-hygroscopic material, and have a radiation absorption characteristicwhich corresponds substantially to predetermined low and high radiationabsorption characteristics of the meat emulsion being pumped through thechamber 14.

The inner, intermediate portion 23 (first sensing means) of the X-raysensor array 21 detects the levels of residual measurement X-rayspassing through and from the chamber 14, and hence through and from theemulsion, to provide respective measurement signals representative ofthose sensed residual measurement X-ray levels.

Similarly, the outer portions 22 (secondary securing means) of the X-raysensor array 21 detect levels of residual reference X-rays passingthrough and from respective reference elements 18, to provide referencesignals representative of those sensed levels of residual referenceX-rays.

Processing means (not shown) located within a housing 130 supportedabove the cabinet 2 by a leg 131 through which cables from the variouselectrical components of the assembly extend to the processor, thenprocesses the measurement and reference signals, to provide interpolatedmeasurement signals which are representative of the specific gravity ofthe meat emulsion within the chamber 14 and which are corrected, usingthe reference signals from the respective reference elements 22, to takeinto account any variable operating parameters of the assembly, forexample, the acceleration voltage applied to the X-ray source 19, theX-ray beam. current of the generator 19, as well as changes in theambient temperature of the monitoring environment.

These corrected, interpolated measurement signals, which arerepresentative of the actual monitored specific gravity of the meatemulsion, are also representative of the fat content of the emulsion.

A video screen 132 is provided in the front wall of the housing 130, fordisplaying the corresponding fat contents of the meat emulsion whosespecific gravity is being monitored.

From time to time, the reference elements 18 need to be re-calibratedabsolutely and this is carried out by moving the X-ray sensor array 21and X-ray source 19 in unison from their operating, monitoring positionat the front of the unit 1, as shown in whole lines in FIG. 2, to acalibration position at the rear of the unit 1, as shown in dashed linesin that FIG. 2.

Additionally or alternatively, such re-calibration may be facilitated bya series of certified references, as shown generally at 31 in FIGS. 1and 2, which can be indexed through the X-ray beam 30 by means of amotorised mechanism indicated diagrammatically at 32.

In the calibration position, the X-ray sensor array is indicatedgenerally at 21′, with respective outer and inner portions thereof beingshown at 22′ and 23′. The diverging X-ray beam is shown at 30′, whilstthe X-ray source is shown at 19′.

Pre-certified calibration elements 18′, corresponding to the referenceelements 18, are moved into the path of the X-ray beam 30′, between theX-ray source 19′ and the X-ray sensor array 21′. These calibrationelements 18′ are certified to correspond to absolutely predetermined lowand high percentage tolerance levels of the radiation absorptioncharacteristics of the meat emulsion and are used to calibrate out anymedium or long term drift which may have occurred in the referenceelements 18 during the monitoring process. As indicated above, thisarrangement may also be used to calibrate the linearity of themonitoring apparatus and assembly, for example, the measurement andreference signal processing means.

Such re-calibration can be programmed to occur at predetermined timeintervals.

Also, the assembly can be arranged to control automatically the flow ofmeat emulsion through the monitoring manifold 11, so that the flow ofmeat emulsion is inhibited or terminated during re-calibration, therebyassuring that all the processed meat product emulsion is monitored forfat content.

It is to be appreciated that the inventive apparatus, assembly andmethod may also be used for monitoring physical properties of otherproducts, with a view to removing contaminants therefrom, particularlysolid contaminants, such as metal, stone, glass, bone and various typesof plastics material.

In a modification of the inventive apparatus, assembly and method, thefirst and second radiation sensing means, such as the X-ray sensingarray 21 of the embodiment described above, may be mounted upon and inclose thermal contact with an isothermal block which is maintained at aconstant temperature, thereby substantially removing any temperaturevariations from that/those components of the inventive apparatus and/orassembly, which might otherwise have a deleterious effect on themonitoring results. In addition to assisting in the maintenance of themonitoring accuracy of the apparatus and method, any input amplifier ofthe processing means and/or its associated circuitry may also be coupledthermally to the isothermal block.

Additionally or alternatively, the temperature of the sensing meansand/or the monitoring chamber may be monitored and used to providesuitable correction signals to the measurement signals.

Although the embodiment described above employs X-rays as a penetrativeand absorptive form of radiation, other forms of such radiation may beused, as may forms of penetrative diffractive radiation.

It is to be appreciated that physical properties of other material, suchas the density, arid hence weight, of tobacco in cigarette rods, mayalso be monitored using the inventive method and apparatus.

What is claimed is:
 1. Dual calibration apparatus (1) for “on-line” orcontinuous monitoring of a physical property of a material, such as thespecific gravity of a processed meat product or the density, and henceweight, of tobacco in a cigarette rod, the apparatus comprising: (a)means (19) arranged to direct radiation into a material having aphysical property to be monitored, (b) first sensing means (23) arrangedto sense levels of residual measurement radiation passing from theirradiated material and to provide respective measurement signalsrepresentative of said sensed levels of residual measurement radiation;(c) reference means (18) which is arranged to be located in the path ofthe radiation, optionally adjacent or within the material whose physicalproperty is to be monitored, and which has radiation absorptioncharacteristics corresponding to predetermined low and high radiationabsorption characteristics of the material whose physical property is tobe monitored: (d) second sensing means (22) arranged to sense levels ofresidual reference radiation passing from said irradiated referencemeans and to provide reference signals representative of said sensedlevels of residual reference radiation; (e) means arranged to processthe measurement and reference signals, to provide interpolatedmeasurement signals; and characterised in that, said reference means(18) comprises a pair of spaced reference standards, a tow radiationabsorption characteristic standard whose absorption characteristiccorresponds to a minimum level of the physical property to be monitoredand a high radiation absorption characteristic standard whose absorptioncharacteristic corresponds to a maximum level of the physical propertyto be monitored, the interpolated results being corrected to take intoaccount any variable operating parameters of the apparatus (1) and beingrepresentative of the actual monitored physical property.
 2. Apparatus(1) according to claim 1, wherein said first sensing means (23)comprises a radiation detector capable of providing measurement signalsrepresentative of the residual measurement levels of radiation receivedthereby from the irradiated material whose physical property is to bemonitored.
 3. Apparatus (1) according to claim 1 or 2, wherein saidsecond sensing means (22) comprises sensing means for each of the pairof spaced reference elements (18).
 4. Apparatus (1) according to any ofclaim 1, 2 or 3, wherein said first and second sensing means (22; 23)are provided in a single array (21).
 5. Apparatus (1) according to anypreceding claim, wherein said reference means (18) comprises a materialwhose radiation absorption characteristic is very close to orsubstantially the same as that of the material whose physical propertyis to be monitored.
 6. Apparatus (1) according to any preceding claim,wherein said radiation direction means comprises an X-ray source (19).7. Apparatus (1) according to any preceding claim, wherein said firstand second sensing means (22; 23) comprises an X-ray detector. 8.Apparatus (1) according to any preceding claim, wherein said radiationdirection means (19) is arranged to provide a diverging beam ofradiation (30) to be directed at and into the material whose physicalproperty is to be monitored.
 9. Apparatus (1) according to any precedingclaim, wherein the geometry of at least those components of theapparatus associated with the monitoring of the material's physicalproperty, is substantially symmetrical, to maintain uniform radiation ofsaid reference and sensing means.
 10. Apparatus (1) according to anypreceding claim further comprising a chamber (14) arranged toaccommodate the material having a physical property to be monitored, theradiation being arranged to be directed into the chamber (14) and,hence, into the material accommodated therein and having a physicalproperty to be monitored.
 11. Apparatus (1) according to claim 10,wherein the chamber (14) comprises a body of substantially uniforminternal cross-section.
 12. Apparatus (1) according to any precedingclaim, wherein the material is arranged to be conveyed passed theradiation (30).
 13. A method of “on-line” or continuous monitoring aphysical property of a material, such as the specific gravity of aprocessed meat product or the density, and hence weight, of the tobaccoin a cigarette rod, which method comprises; directing radiation (30)into a material having a physical property being monitored; sensinglevels of residual measurement radiation passing from the irradiatedmaterial, providing measurement signals representative of said sensedlevels of residual measurement radiation; locating in the path of theradiation (30), optionally adjacent or within the material whosephysical property is being monitored, reference means (18) havingradiation absorption characteristics corresponding to predetermined lowand/or high radiation absorption characteristics of the material whosephysical property is to be monitored; sensing the level of residualreference radiation passing from said irradiated reference means (18);providing reference signals representative of said sensed levels ofresidual reference radiation; processing the measurement and referencesignals to provide interpolated measurement signals; and characterisedin that, said reference means (18) comprises a pair of spaced referencestandards, a low radiation absorption characteristic standard whoseabsorption characteristic corresponds to a minimum level of the physicalproperty to be monitored and a high radiation absorption characteristicstandard whose absorption characteristic corresponds to a maximum levelof the physical property to be monitored, and correcting theinterpolated results to take into account any sensed variation of theoperating parameters and thereby representing the actual monitoredphysical property.
 14. A method according to claim 13, wherein theradiation (30) is directed into the material whose physical property isbeing monitored as a diverging bean.
 15. A method according to claim 13or 14, wherein the levels of residual measurement radiation are sensedby a radiation detector (21) providing measurement signalsrepresentative of the residual measurement levels of radiation receivedthereby from the irradiated material whose physical property is beingmonitored.
 16. A method according to any of claim 13, 14 or 15, whereinthe level of residual reference radiation passing from the pair ofirradiated spaced reference elements (18), is sensed by respective onesof a pair of sensing means (22).
 17. A method according to any of claims13 to 16, wherein said reference means (18) is provided by a materialwhose radiation absorption characteristic is very close to orsubstantially the same as the material whose physical property is beingmonitored.
 18. A method according to any of claims 13 to 17, wherein theradiation (30) is X-ray radiation.
 19. A method of calibrating saidreference means of the apparatus (1) according to any of claims 1 to 12,which method comprises locating between a or the radiation source (19)and at least said second sensing means (22) at least one pre-certifiedcalibration element (18′) certified to correspond to absolutelypredetermined low and high percentage tolerance levels of the radiationabsorption characteristic of the material whose physical property is tobe monitored, generating a signal to correspond to radiation passingfrom said at least one pre-certified calibration element (18′) andemploying that signal to calibrate out any medium or long term drift insaid reference means (18).
 20. A method according to claim 19, whereincalibration of said reference means is programmed to run atpredetermined time intervals.
 21. A method according to claim 19 or 20,wherein calibration is carried out remote from the operationalmonitoring position.
 22. A method according to claim 19, 20 or 21,wherein calibration is carried out using a series of certifiedreferences (18′) indexed through the path of the radiation (30).
 23. Amethod according to claim 22, wherein indexing of the series ofcertified references (18′) is effected by a motorised mechanism.